1. Field of the Invention
The present invention relates to a light projection method and apparatus. In particular, this invention provides a light projection method and apparatus for an optical mouse.
2. Description of the Related Art
When an optical mouse is moved to an image detection surface, the optical mouse detects the image located on the concave and the convex of the image detection surface through an image detection unit. Then, the optical mouse executes an optical energy level transformation via a circuit unit to calculate the displacement and the direction of displacement. After that, any movements a user performs on the optical mouse are mirrored by the cursor on a display unit.
Please refer to FIG. 1, which shows an optical mouse of the prior art. The optical mouse comprises a light projection apparatus 8, a light source 2, an image-forming lens 3 and an image detection unit 4. The light projection apparatus 8 comprises a light-guiding body that comprises a convex lens surface 80, a first incline surface 81, a second incline surface 82 and a light-emitting surface 83. The first incline surface 81 corresponds to the convex lens surface 80. The second incline surface 82 corresponds to the first incline surface 81. The light-emitting surface 83 corresponds to the second incline surface 82 and faces towards an image detection surface 5. A transparent medium 6, such as a glass, is disposed on the image detection surface 5. The light emitting from the light source 2 enters the light-guiding body through the convex lens surface 80. The light is reflected from the first incline surface 81 to the second incline surface 82. Next, the light is reflected by the second incline surface 82 to form a light beam L and is slantwise transmitted to the transparent medium 6. The light beam L passes through the transparent medium 6 and is slantwise projected to the image detection surface 5.
Because the intersection point of the light beam L and the image detection surface 5 is not located on the detection area 50 of the image detection light axis X formed by the image-forming lens 3 and the image detection unit 4, the image detection unit 4 can't detect the exact location of the image at the detection area 50 of the image detection surface 5. Therefore, when the optical mouse is moved on the image detection surface 5, the movement of the cursor displayed on the display unit is not sensitive enough and, in the worst case, the cursor can't be moved.
Please refer to FIG. 2, which shows an optical mouse of another prior art. The optical mouse comprises a light projection apparatus 9, a light source 2, an image-forming lens 3 and an image detection unit 4. The light projection apparatus 9 comprises a light-guiding body that comprises a convex lens surface 90, a first incline surface 91, a light-emitting surface 93 and a light splitting surface 94. The first incline surface 91 corresponds to the convex lens surface 90. The light-emitting surface 93 corresponds to the first incline surface 91. The light splitting surface 94 corresponds to the light-emitting surface 93 and the first incline surface 91. An opening 95 is formed between the light splitting surface 94 and the light-emitting surface 93 and faces toward an image detection surface 5. The light splitting surface 94 also faces towards the image detection surface 5. A transparent medium 6, such as a glass, is disposed on the image detection surface 5. The light emitting from the light source 2 enters the light-guiding body through the convex lens surface 90. The light is reflected from the first incline surface 91 to the light splitting surface 94. Next, the light is reflected by the light splitting surface 94 to form a light beam L and is vertically transmitted to the transparent medium 6. The light beam L passes through the transparent medium 6 and is vertically projected to the detection area 50 of the image detection surface 5.
Because the intersection point of the light beam L and the image detection surface 5 is located on the detection area 50 of the image detection light axis X formed by the image-forming lens 3 and the image detection unit 4, the image detection unit 4 can detect the exact location of the image in the detection area 50 of the image detection surface 5. However, when the light beam L is vertically projected to the image detection surface 5, the contrast between the concave and the convex of the image detection surface 5 is not obvious due to the image detection surface 5 being an uneven surface. This increases the difficulty of the image being detected by the image detection unit 4. As such, when the optical mouse is moved over the image detection surface 5, the movement of the cursor displayed on the display unit is not replicated. Especially, the movement of the cursor becomes uncontrollable when the optical mouse is rapidly moved over the image detection surface 5.